Rio Tinto has created a rose gold and pink diamond ingot to commemorate the opening of its underground Argyle diamond mine.

The underground mine's opening was announced in April and is anticipated to help extend the mining potential of Argyle diamonds until 2020. The mine is the first of its kind in Western Australia and will use block caving technologies to help boost output, taking the average annual production of the mine to about 20 million carats per year.

As a celebration of the opening Rio Tinto has created 168 limited-edition pink diamond ingots, each hand-set with six Argyle diamonds into a 1oz bed of rose gold from The Perth Mint. Each ingot is also individually numbered.

The Argyle Diamond Mine managing director Kim Truter said: “We are delighted to partner with The Perth Mint on the exclusive release of this distinctive investment piece. It is a beautiful symbol of the unique Argyle story and the recent milestone commencement of underground mining."

Each ingot is valued at AU$4,880 (£2,974) all are set to be released for sale worldwide. Each ingot will be accompanied by a numbered certificate of authenticity.